
^57 



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opy 1 

The Ohio State University Bulletin 

Volume XXII MAY, 1918 Number 28 



EFFECT OF GAS PRESSURE ON 

Natural Gas Cooking 
Operations in the Home 



BASED ON / — .^ ^ A 



TESTS MADE IN THE LABORATORY 

OF THE 

DEPARTMENT OF HOME ECONOMICS 

THE OHIO STATE UNIVERSITY 

Columbus. Ohio 



Under the Direction of 

EDNA NOBLE WHITE, Head of Department of Home Economics 

GRACE LINDER, Instructor in Home Economics 

AND 

SAMUEL S. WYER, Consulting Engineer. Columbus. Ohio 



PUBLISHED BY THE UNIVERSITY AT COLUMBUS 

Entered as second-class matter November 17, 1905, at the postofBce at Columbus, Ohio 
under Act of Congress, July 16, 1894 



INTRODUCTION 

The determination of "what is usable natural gas pressure for 
cooking service" has long been desirable. Since more than 36 per 
cent of all of the natural gas consumers in the United States live 
in Ohio, and 73 per cent of Ohio's population are dependent on 
natural gas for their cooking service, it became evident that the 
problem had a vital relation to the homes of the State, and that the 
Home Economics Department should undertake to obtain accurate 
data to answer this much discussed and little understood question. 

The primary object of the tests was to duplicate household 
operations rather than fancy laboratory conditions. Although a 
water calorimeter, such as described in Vol, 1, page 699, of the Pro- 
ceedings of the American Gas Institute for 1906, would give a 
slightly higher efficiency for the burner, we thought it fairer to 
measure the eflficiency with an ordinary cooking vessel rather than 
with the more refined calorimeter, which would be of no interest to 
the gas user. We believe that utility or usability may be of more 
importance than mere efficiency; tests were therefore made to de- 
termine exactly what results could be obtained with ordinary 
kitchen utensils, from the very lowest to the highest pressures that 
might be found in a natural gas distributing plant. 

The experimental results obtained are given in Part 1, pages 
3 to 17. The conclusions to be drawn from the tests are given on 
pages 18 and 19. Some of the fundamental principles that must be 
understood to secure a proper conception of the natural gas pres- 
sure question are given in Part II, pages 20 to 27. 

The routine work of the tests, under constant supervision, was 
carried on by the Misses Biebricher, Erskine, Kirkpatrick, Nolan 
and Steiger, members of the Department's senior class. 

In conclusion we wish to emphasize that the tests were made 
to determine what were usable natural gas pressures and not rel- 
ative merits of particular stoves. 



Columbus, Ohio 



May 9, 1918. *•••* - ^^ ^ 



f^^^ TABLE OF CONTENTS 

PART I 
EXPERIMENTAL DATA TO DETERMINE EFFECT OF PRES- 
SURE ON NATURAL GAS COOKING OPERATIONS 

Section Page 

1. Description of Apparatus 3 

2. Importance of Vessel Position 3 

3. Efficiencies at Various Pressures 6 

4. Boiling Potatoes at Various Pressures , 12 

5. Frying Potatoes at Various Pressures '. 12 

6. Cooking Meat at Low Pressures 12 

7. Baking Tests £|t Low Pressures 13 

8. Accuracy of Meter Registration at Low and Various Gas Pressures 14 

9. Conclusions 18 

PART II 

FUNDAMENTAL PRINCIPLES UNDERLYING NATURAL 
GAS PRESSURE QUESTION 

Section Page 

10. Definition of "Natural Gas" 20 

11. What Makes Gas Pressure 20 

12. Gage Pressure 20 

13. Atmospheric Pressure 21 

14. Barometric Changes Make More Difference on Total Pressure Than 
Gage Pressure Variation 21 

15. Absolute Pressure .., 21 

16. Differential Pressure 22 

17. What Makes Gas Flqw? 23 

18. Effect of Pressure on Gas Volume ^ 24 

19. Effect of Temperature on Gas Volume 24 

20. Standard Conditions 24 

21. Heat Unit 24 

22. Heating Value 25 

23. Effect of Pressure or Temperature Changes on Heating Value of Gas.... 25 

24. Combustion of Natural Gas 26 

25. Action of Gas Mixer 26 

26. Efficiency 27 

27. Efficacy 27 

28. Cooking and Heating Distinguished 27 

LIST OF ILLUSTRATIONS 

Fig. Page 

1. Diagram of Apparatus Used in Cooking Tests 3 

2. Photograph of Apparatus Used in Cooking Tests 4 

3. Photograph of Drilled Burner 5 

4. Photograph of Slotted Burner ^ 5 

5. Curves Showing Gas Required to Boil Potatoes at Various Pressures.. 7 

6. Curves Showing Gas Required to Fry Potatoes at Various Pressures.. 8 

7. Curves Showing Variation in Time Required to Boil Potatoes at Vari- 
ous Pressures 9 

8. Curves Showing Variation in Time Required to Fry Potatoes at Vari- 
ous Pressures 10 

9. Curves Showing Efficiencies at Various Pressures 11 

10. Diagram Showing Relation of Atmospheric and Gage Pressure 21 

11. Curve Showing Effect of Pressure on Gas Volume 22 

12. Curve Showing Mean Monthly Temperatures of Natural Gas 23 

13. Diagram Showing Construction of Ordinary Gas Mixer 26 

14. Diagram Showing Construction of Gas Mixer with Adjustable Spud.... 27 



PART I 

EXPERIMENTAL DATA TO DETERMINE EFFECT OF PRES- 
SURE ON NATURAL GAS COOKING OPERATIONS 
§1. Description of Apparatus. 

The apparatus used in the tests is shown in Figures 1 and 2. 
A 10 cu. ft. meter prover is shown at the right. The pressures were 
increased by placing weights on top of the meter prover, as shown. 
The gas from a service line was passed into the meter prover bell 
and the weights and counter weights were then adjusted to give the 
desired pressure. 

FIGURE I 



DIAGRAM OF APPARATUS USED 



COOKING 




Bi/rner 







The gas was measured in an ordinary domestic natural gas 
mjeter. This had a differential pressure gage attached to the top, 
as shown, to indicate the pressure drop over the meter, or, in other 
words, the amouHt of gas pressure necessary to operate the meter, 
this was found to be .1 inch of water pressure. The pressure at 
the cooking fixtures was determined by the U-tube pressure gage, 
and measured in ounces per square inch by means of a scale grad- 
uated in ounces. 

Referring to Fig. 2, the stove at the extreme left is a natural 
gas range, with adjustable spud similar to the one shown in Fig. 14. 
The stove in the middle is a range designed for manufactured gas, 
with a non-adjustable spud, having a No. 47 orifice, similar to that 
shown in Fig. 13. The hot plate at the right is simply an ordinary 
natural gas hot plate with a non-adjustable spud, similar to that 
shown in Fig. 13. 



§2. Importance of Vessel Position. 

For cooking operations it is only the tip of the flame that can 
be used for effective service. If the flame is short and the vessel 



FIG. 2 
PHOTOGRAPH OF APPARATUS USED IN COOKING TESTS 




FIG. 3 

PHOTOGRAPH OF DRILLED BURNER WITH NAIL OR 

WIRE INSERTS TO SUPPORT COOKING VESSEL 

FOR LOW PRESSURE NATURAL GAS SERVICE. 




FIG. 4 

PHOTOGRAPH OF SLOTTED BURNER WITH THREE 
PIECES OF SHEET IRON FOR SUPPORTING COOK- 
ING VESSEL FOR LOW PRESSURE NATURAL 
GAS SERVICE. 




is so far away that the hot point of the flame does not come close 
to the vessel, satisfactory results cannot be obtained. If the flame 
is very long in order to reach the high vessel, the stove will be 
wasteful in the use of gas. 

The following experiment brings out this feature in a rather 
startling manner. This consisted merely in placing a standard 
granite-ware vessel containing 7 lbs. of water on top of each of the 
three stoves as shown, and with .8 oz. pressure, noting the length 
of time required to bring the water to a vigorous boil, and the gas 
consumption necessary to accomplish this. The results were as 
follows : 

Natural Manufactured Hot 

Gas Range Gas Range flate 

Vessel distance, inches 2.1 1.8 1.5 

Length of flame, inches .6 .6 .3 

Cu. ft. of gas _ 6.9 3.6 3.9 

Time in minutes 47 16 49 

In order to bring the vessel to the best operating position for 
short flames all that is necessary is some device that will hold the 
vessel the correct distance from the burner. With the drilled type 
of burner this can be easily accomplished by removing the stove 
top and inserting three nails or pieces of wire, as shown in Fig. 3, 
and then placing the vessel on the top of these. With the slotted 
type of burner, remove the stove top and simply insert three pieces 
of sheet iron or heavy tin, as shown in Fig. 4, and then place the 
vessel on the top of these. This is the only change necessary in 
order to secure satisfactory cooking results with the ordinary 
stove with low pressures and the resulting short flame lengths. 

With low pressures, we found that no perceptible change could 
be made in the combustion conditions by attempting to adjust the 
air shutter. That is, entirely satisfactory results were obtained 
with the air shutter wide open, without any adjustment whatsoever. 

§3. Efficiencies at Various Pressures. 

In order to determine the efl[iciencies of the three stoves at 
various pressures, a granite-ware kettle — having a diameter of 8I/2 
in. and height of 6 in., and of the form shown in Fig. 2 — containing 
6 lbs. of water was heated, and the number of cu. ft. of gas required, 
to raise this water to 200 degrees F. was noted. The heating value* 
of the gas was determined in a gas calorimeter and the gas used m 
these tests averaged 1,000 B. t. u. per cu. ft. 

Since the B. t. u. is merely the amount of heat required to raise 
one lb. of water one degree F., multiplying the number of pounds 
of water by the total rise in temperature would give the number 
of heat units actually delivered to the cooking vessel. This figure 
in turn divided by the number of heat units in the gas used in heat- 
ing the water will represent the efficiency, as defined in Sec. 26. 
The efficiency tests of the three types of stoves, at the various 
pressures, are tabulated in Table I, page 15 and shown in graphical 
form in Fig. 9, page 11. 



FIGURE 5 

CURVES SHOWING AMOUNT OF GAS REQUIRED TO 

BOIL 2 LBS. OF OLD UNREELED POTATOES ON 

THREE TYPES OF GAS STOVES 

AT VARIOUS PRESSURES 



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FIGURE 6 

CURVES SHOWING AMOUNT OF GAS REQUIRED TO 

FRY 2 LBS. OF OLD RAW THINLY SLICED POTATOES 

ON THREE TYPES OF GAS STOVES 

AT VARIOUS PRESSURES 



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BOIL 2 LBS. OF OLD UNREELED POTATOES ON 

THREE TYPES OF GAS STOVES 

AT VARIOUS PRESSURES 



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FRY 2 LBS. OF OLD RAW THINLY SLICED POTATOES 

ON THREE TYPES OF GAS STOVES 

AT VARIOUS PRESSURES 



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12 

§4. Boiling Potatoes at Vsurious Pressures. 

In this test two pounds of old, unpeeled potatoes were cooked 
in 6 lbs. of water, in an ordinary granite-ware kettle having a 
diameter of 8V2 in. and height of 6 in., and of the form shown in 
Fig. 2. 

The data obtained on the three stoves at various pressures are 
shown in tabulated form in Table III, page 17 and in graphical form 
in Figs. 5 and 7, pages 7 and 9. 

§5. Frying Potatoes at Various Pressures. 

In this series of tests 2 lbs. of thin sliced, old, raw potatoes 
were fried, with an ample supply of hot lard, in an ordinary pressed 
steel skillet. 

The data obtained on the three stoves at various pressures are 
shown in tabulated form in Table II, page 16 and in graphical form 
in Figs. 6 and 8, pages 8 and 10. 

§6. Cooking Meat at Low Pressures. 

In this test 2 lbs. of ground round beefsteak was fried in an 
ordinary pressed steel skillet, with a gas pressure of .2 oz. The 
data obtained for the three stoves were as follows : 

Frying Beefsteak 

Natural Manufactured 

Ckis Oas Hot 

Range Range Plate 

Weight, ground Round Steak 2 lb. 2 lb. 2 lb. 

Gas pressure in ounces per sq. in. .2 .2 .2 

Cu. ft. of gas 1.85 1.675 1.225 

Time in minutes 14 14 27 

Flame length in inches 3 .3 .2 

Skillet distance, inches 6 .6 .3 

Barometric pressure in inches 

mercury 29.37 29.37 29.37 

In the following test 1 lb. of thick Porterhouse beefsteak was 
pan-broiled in an ordinary pressed steel skillet, with a gas pressure 
of .2 oz. The data obtained for the three stoves were as follows : 

Pan-Broiled Beefsteak 

Natural Manufactured 

Gas Gas Hot 

Range Range Plate 

Weight, Porterhouse Steak 1 lb. 1 lb. 1 lb. 

Gas pressure in ounces per sq. in. .2 .2 .2 

Cu. ft. of gas 9 .6 .7 

Time in minutes 7. 7. 16. 

Flame length in inches 2 .3 .2 

Skillet distance, inches 6 .6 .3 

Barometric pressure in inches 

mercury 29.18 29.18 29.18 



13 

§7. Baking Tests at Low Pressures. 

In baking 1 lb. loaves of white bread made up of two-thirds 
wheat and one-third barley flour, at .5 oz. and 4 oz. pressures, the 
following results were obtained in the bakers of the natural gas 
and manufactured gas ranges: 

Natural Oas Manufactured Qag 

Range Range 

Time Cu. ft. Time Cu. ft. 
in min. Gas in min. Gas 
.5 oz. Pressure — 

Heating oven ready to receive bread 26 7.5 16 3.2 
Baking bread 32 3.25 33 6 



Totals 58 10.75 49 9.2 



4 oz. Pressure 



Heating oven ready to receive bread 14 6 7 2.2 

Baking bread 32 4.2 32 7.2 



Totals 46 10.2 39 9.4 



14 

§8. Accuracy of Meter Registration at Low and Various Gas 
Pressures. 

The popular belief is that meters run faster when the pressure 
is low than when the pressure is high. This is contrary to the facts. 
Variation in pressure makes no appreciable difference in the regis- 
tration of the meter, the meter merely registering — within a 
reasonable limit of tolerance* — the amount of gas that passes, and 
this is neither increased nor decreased by changes in pressure.** 

A No. 1 Iron Clad, Pittsburg Meter Co., Dry Meter, No. 298598, 
was used for measuring the gas in these tests. This was proved 
for accuracy before the tests were started. The meter had been 
in use for about two years prior to the tests and was in no way 
specially prepared by adjustment or lubrication for this work, other 
than merely to check its accuracy against a certified meter prover. 

After the cooking tests were completed the meter prover used 
for adjusting the pressures — shown in Fig 2 — was filled with nat- 
ural gas which was then allowed to stand for several hours, until 
it acquired the room temperature. The gas from this meter prover 
was then passed through this meter at various pressures, through 
the middle burner — having a No. 47 spud opening — of the Peerless 
range, giving the following results : 

Per cent. 
Pressure in oz. No. minutes Cu. ft. gas Cu. ft. gas Error of 

per sq. inch to pass 1 cu. ft. by meter by m^ter prover meter 

.2 10.5 1 1.01 1% slow 

.4 6.3 1 1.01 1% slow 

.6 5.4 1 .99 1% fast 

.8 5.0 1 .98 2% fast 

1.0 4.0 1 1.01 1% slow 

1.5 3.2 1 1.00 

2.0 2.5 1 .99 1% fast 

3.0 2.0 1 1.01 1% slow 

4.0 1.8 1 1.00 

5.0 1.5 1 1.01 1% slow 

The above data show that low pressures do not make the meter 
run faster. Incidentally, the number of minutes required to run 
1 cu. ft. of gas becomes an index of the leakage tendencies ?t vari- 
ous pressures. Since it takes about one-half the time to pass the 
same amount of gas at 4 oz. as at 1 oz., it is evident that the rate of 
leakage, on the consumer's premises and on the company's distribut- 
ing plant, would be about twice as great at 4 oz. pressure as it 
would be at 1 oz. pressure. 

*The Ohio Laws fix the limit of tolerance at 3 per cent, fast or 3 per cent, slow for gas 
meters. That is, a meter that is within not to exceed 3 per cent, fast or 3 per cent, slow is 
regarded as commercially accurate. 

**The same conclusion was reached in a report published by the Kansas Public Utilities 
Commission, as Engineering Bulletin No. 2, of the University of Kansas, on "Natural Gas: 
Its Properties, Its Domestic Use, and Its Measurement by Meters," under date of July 1, 1912. 



15 

TABLE I 

Efficiencies obtained with three different types of gas stoves 
in heating 6 lbs. of water from the faucet temperature to 200 
degrees F., at various pressures, using natural gas having a heating 
value of 1,000 B. t. u. per cubic foot. The vessel distances were 
the same as those given on page 17 for the various pressures. 



Pressures in ounces 

per square inch 2 .4 .6 .8 1. 1.5 2. 3. 4. 5. 



NATURAL Gas Range. 

Final temperature of 

water 200 200 200 200 200 200 200 200 200 200 

Initial temperature of 

water 76 78 74 78 78 76 76 76 79 77 

Rise of water 124 122 126 122 122 124 124 124 121 123 

B. t. u. in water 744 732 756 732 732 744 744 744 726 738 

Cu. ft. of gas 1.97 2.3 2.1 2.55 2.6 2.5' 3.7 5.5 5.6 5.1 

B. t. u. in gas 1970 2300 2100 2550 2600 2500 3700 5500 5600 5100 

Efficiency*% 37 32 36 29 28 30 20 14 13 14 



MANUFACTURED Gas Range. 

Final temperature of 

water 200 200 200 200 200 200 200 200 200 200 

Initial temperature of 

water 76 78 78 77 78 75 75 78 73 77 

Rise of water 124 122 122 123 122 125 125 122 127 123 

B. t. u. in water 744 732 732 738 732 750 750 732 762 738 

Cu. ft. of gas 1.71 1.87 1.9 2.2 3.1 2.7 2.55 2.1 2.6 2.45 

B. t. u. in gas 1710 1870 1900 2200 3125 2700 2550 2100 2600 2450 

Efficiency*% 43 40 35 33 23 27 29 35 29 30 



HOT PLATE. 

Final temperature of 

water 200 200 200 200 200 200 200 200 200 200 

Initial temperature of 

water 78 72 78 76 75 72 76 76 75 78 

Rise in water 122 128 122 124 125 128 124 124 125 122 

B. t. u. in water 732 768 732 744 750 768 744 744 750 732 

Cu. ft. of gas 2.45 1.825 1.65 1.65 2.125 2.05 1.9 2.95 2.08 2. 

B. t. u. in gas 2450 1825 1650 1650 2125 2300 1900 2950 2080 2000 

Efficiency* % 21 42 44 45 36 33 39 26 35 36 

*For definition of term "Efficiency" and method of calculation see Sections 3 and 26. 



16 



4. 


4.3 


3.45 


3.72 


4.8 


4.6 


5.65 


5.5 


5.9 


21 


21 


16 


16 


16 


18 


17 


20 


24 


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1.1 


1. 


1. 


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2.1 


2.1 


2.1 



TABLE II 

Data obtained in frying 2 lbs. of thin sliced, old, raw potatoes 
in an ordinary pressed steel skillet, with an ample supply of hot 
lard, on three different types of stoves, with natural gas at various 
pressures and having a heating value of 1,000 B, t. u. per cubic foot. 



Pressures in ounces 

per square inch 2 .4 .6 .8 1. 1.5 



NATURAL Gas Range. 

Cu. ft. of gas 3.1 

Time in minutes 23 

Flame length in inches .6 

Skillet distance, inches .6 
Barometric pressure in 

inches mercury 29.44 28.85 29.32 29.06 29.21 29.34 29.4 29.34 29.34 29.69 



MANUFACTURED Gas Range. 

Cu. ft. of gas 2.44 

Time in minutes 22 

Flame length in inches .3 
Skillet distance, inches 1.1 
Barometric pressure in 

inches mercury 29.42 29.21 29.34 29.16 29.24 29.34 29.26 29.41 29.33 29.21 



HOT PLATE. 

Cu. ft. of gas 1.45 1.975 

Time in minutes 30 28 

Flame leng-th in inches .3 .3 

Skillet distance, inches .3 .7 
Barometric pressure in 

inches mercury 29.225 29.2 



3.6 


3.75 


4.675 


3.76 


4.175 


3.2 


4.1 


4.2 


3.8 


20 


19 


18 


21 


21 


22 


15 


19 


17 


.5 


.6 


.7 


.7 


.7 


.7 


.7 


.8 


.9 


1.1 


1.5 


1.6 


1.7 


1.7 


1.7 


1.7 


1.7 


1.7 



1.7 


2.65 


2.9 


2.125 


2.3 


2.8 


2.71 


2.5 


30 


25 


19 


21 


21 


22 


19 


18 


.3 


.5 


.6 


.6 


.6 


.6 


.6 


.7 


.7 


.7 


1.7 


1.7 


1.7 


1.7 


1.7 


1.7 


'.56 


29.18 


29.07 


29.15 


29.28 


29.41 


28,98 


29.21 



17 



TABLE ill 



Data obtained in boiling 2 lbs. of old, unpeeled potatoes in 
6 lbs. of water, in an ordinary granite ware kettle, on three dif- 
ferent types of stoves, with natural gas at various pressures and 
having a heating value of 1,000 B. t. u. per cubic foot. 



Pressures in ounces 
per square inch 



.4 



.6 



1.5 



3. 



4. 



NATURAL Gas Range. 



Cu. ft. of gas 5. 

Time in minutes 47 

Flame length in inches .6 
Vessel distance, inches .6 
Barometric pressure in 
inches mercury 29.42 



5.5 


6.62 


6. 


7.15 


7.15 


8.27 


9.35 


9.35 


10. 


33 


32 


29 


30 


24 


34 


35 


38 


37 


.7 


.7 


.7 


.8 


.8 


.9 


1. 


1. 


1.1 


1. 


1. 


1.2 


1.2 


1.2 


2.1 


2.1 


2.1 


2.1 



29.20 29.33 29.04 29.22 29.34 29.40 29.34 29.34 29.68 



MANUFACTURED Gas Range* 

Cu. ft. of gas 4.83 5.4 5.9 6.45 6.55 

Time in minutes 45 33 30 27 26 

Flame length in inches .3 .5 .6 .7 .7 

Vessel distance, inches .5 .9 1.3 1.6 1.7 
Barometric pressure in 

inches mercury... 29.425 29.215 29.18 29.16 29.22 



6.4 
31 

.7 
1.7 



5.19 
40 

.7 
1.7 



5.3 
23 

.7 
1.7 



5.7 

27 

.8 

1.7 



6.1 

25 

.9 

1.7 



29.36 29.29 29.34 29.23 29.21 



HOT PLATE. 



Cu. ft. of gas 4.29 

Time in minutes 85 

Flame length in inches .3 
Vessel distance, inches .3 
Barometric pressure in 
inches mercury 29.32 



4.05 


4. 


4. 


4.75 


4.85 


3.9 


4.45 


4.9 


4.4 


61 


47 


40 


41 


37 


39 


34 


35 


32 


.3 


.3 


.5 


.6 


.6 


.6 


.6 


.6 


.7 


.7 


.7 


.7 


1.7 


1.7 


1.7 


1.7 


1.7 


1.7 



29.20 29.56 29.29 29.06 29.34 29.28 29.41 28.98 29.21 



•This stove was designed for manufactured gas and gave these results with natural gas without any 
change in stove construction, or adjustment. 



§9. Conclusions. 

1. — Satisfactory cooking operations in frying potatoes, boiling 
potatoes, frying beefsteak, and pan-broiling beefsteak can be car- 
ried on with .2 oz. natural gas pressure. 

2. — The changes in vessel position necessary to permit satis- 
factory operation at pressures as low as .2 oz. are easy to make 
and require no special changes in existing stoves. 

3. — Bread can be satisfactorily baked with .5 oz. natural gas 
pressure. 

4 — Natural gas stoves are not properly constructed to use 
natural gas efficiently at high pressures, nor satisfactorily at low 
pressures. 

5 — At high pressures natural gas stoves are inefficient and 
therefore wasteful in their use of gas. 

6 — The burners on natural gas stoves are too low. 

7 — The holes in the spuds of natural gas stoves are too small. 

8 — Long flames for cooking operations are wasteful. 

9 — The maximum results are obtained with many short flames 
rather than a few long flames. 

10 — A strong draft of air may deflect the flame away from 
cooking vessel so as to seriously interfere with and in many cases 
stop cooking. 

11 — Where two flames strike each other, due to the fact that 
openings are too close in burner, poor combustion will result. This 
will produce a luminous flame which will in turn result in a smok- 
ing burner. Neither air nor gas adjustment can overcome this. 

12 — Drilled burners are better than slotted burners, because 
there is less hkelihood of two adjacent flames striking against each 
other, therefore producing imperfect combustion conditions. 

13 — Natural gas cook stoves should not be furnished with solid 
stove tops since this suggests the carrying on of cooking operations 
on top of the stove, rather than with the vessel in the proper posi- 
tion. 

14 — At low pressures no perceptible change can be made in the 
combustion conditions by adjusting the air shutter. The best con- 
ditions obtained were with the shutter wide open. 



19 

15 — Too much heat is used in most cooking operations, correct 
application is more important than mere intensity. 

16 — ^The natural gas pressures carried in most natural gas dis- 
tributing plants are too high for efficient operation. 

17 — Meter registration is approximately correct regardless as 
to variation in pressure. That is, meters do not run faster when 
the pressure is low. 

18 — Lowering the temperature of natural gas increases its 
heating value per cubic foot. Natural gas has a temperature about 
25 degrees lower in the coldest month in winter than in the hottest 
month in summer, and the heating value per cubic foot due to 
change in temperature is therefore about 5 per cent higher in the 
coldest month in winter than in the warmest month in summer. 

19 — The maximum possible variation of heating value due to 
variation in gage pressure would make the heating value during 
the low pressure periods in winter less than 3 per cent lower than 
during the high pressure period in summer, 

20 — Since the heating value increase due to low temperature of 
gas in winter more than offsets the possible decrease in heating 
value due to low pressure, the practical effect of the two is that 
the heating value per cubic foot of natural gas as served in the 
winter under low pressures and low temperature is higher than that 
served in the summer under higher pressures and higher temper- 
ature. 

21 — Variation in barometer from day to day may make more 
of a change in the heating value of gas than any possible variation 
in gage pressure. 

22 — Better and more efficient service could be rendered if nat- 
ural gas pressures were generally lowered to probably 2 oz. rather 
than increased to 4 oz, or above. 

23 — The lowering of natural gas distributing pressures to ap- 
proximately 2 oz. would produce more efficient and satisfactory 
operating conditions for the consumer, would greatly curtail the 
leakage on the consumer's premises, which is paid for by the con- 
sumer, and would also substantially lower the leakage in the gas 
company's distributing plant. 



20 



PART II 



FUNDAMENTAL PRINCIPLES UNDERLYING NATURAL GAS 
PRESSURE QUESTION 

§10. Definition of "Natural Gas." 

Natural gas is a highly combustible gas made by a secret pro- 
cess of nature. It is not a chemical compound— as popularly sup- 
posed — but a mechanical mixture of several combustible and diluent 
gases and vapors thoroughly diffused— that is, thoroughly mter- 

mixed through each other, the number and exact proportion of the 

various crude natural constituents varying for the different locali- 
ties and somewhat during the working lives of individual wells. 

§11. What Makes Gas Pressure. 

Natural gas is a fluid composed of a large number of molecules 
which are vehicles of energy continually in motion and having an 
inherent tendency to get farther and farther apart. The range of 
motion of the molecules is limited only by the volume of the closed 
containing vessel in which they constantly move to and fro. That 
is the molecules are in a state of constant bombardment against 
each other and against the sides of the containing vessel. 

Natural gas pressure is the result of the combined efforts of all 
the moving molecules in the gas trying to get farther and farther 
apart ; that is, a mass of gas enclosed in a vessel expands and fills 
it and being restrained from further expansion, it exercises a pres- 
sure against the walls of the vessel. This pressure is the same m 
all directions on equal areas of surface. Contracting the volume of 
gas increases the intensity of its internal molecular motion and 
therefore increases its pressure. 

With a given mass of gas any increase in volume of containing 
vessel will give the molecules more range of motion and thereby 
lower the pressure. 

Thus, if a part of a given mass of gas is removed from a closed 
vessel or reservoir the remaining mass of gas will expand instanter 
and keep the vessel or reservoir filled, but at a lower pressure. 

§12. Gage Pressure. 

This is simply the pressure indicated by a pressure gage. Two 
o-eneral classes of gages are used for measuring gas pressure : 

a— Spring Gages— Where the effect of the pressure ex- 
erted against some form of spring is made to move a pointer 
over a graduated dial or scale. 

b— Fluid Gages— Where the effect of the pressure is indi- 
cated by the height of the column of fluid in a "U" shaped 
tube One side of the "U" shaped tube is open to the atmos- 
phere and the other is attached to the pipe where the pres- 
sure is to be measured. The gas pressure in this pipe then 
lowers the fluid in one side of the tube and raises it m the other. 
The total difference in the heights of the fluid on the two sides 



21 



FIGURE 10 

represents the total fluid pressures as shown in Fig. d'agram show- 
1, page 3. When no pressure is applied to such a '^atmospheric '^ 
"U" tube gage other than the prevaihng atmospheric cAcfl preIsure 
pressure, the hquid will stand at the same level in 
bothtubes. _ rp£ss^/Ff 

The pressures m natural gas distributing plants i ^oz=J^0 -^ 
are almost universally measured in ounces per square ""- 
inch, while the pressures in manufactured gas dis- 
tributing plants are measured in inches of water, 1 
oz. equalling 1.73 inches of water. 

Where the word pressure occurs in ordinances 
or rules it invariably means gage pressure. 



§13. Atmospheric Pressure. 

Atmospheric pressure is measured by a bar- 
ometer — usually in inches of mercury, one inch of 
mercury equalling .49 lb. per square inch pressure — 
and is synonymous with barometric pressure. 

Sea level is the datum from which atmospheric 
pressures are reckoned. At that point dry air at 
82 degrees Fahrenheit exerts a pressure of 14.7 lbs. 
per square inch. 

This pressure varies with altitude and temper- 
ature, the pressure decreasing with an increase in 
altitude or temperature. 14.4 lbs. represents a fair 
average barometric pressure for most natural gas 
using communities. 

§14. Barometric Changes Make More Di£Ference On 
Total Pressure Than Gage Pressure Variation. 

On account of the changing atmospheric condi- 
tions the barometric pressure of gas varies from day 
to day, and from hour to hour on the same day, thus, 
during these tests the barometric pressure varied 
from 29.69 to 28.85 inches of mercury, the equiva- 
lent of .41 lbs. — 6 oz. — or considerably more than 
the entire range in gage pressure. 

§15. Absolute Pressure. 

This is the sum of the gage pressure and the baro- 
metric pressure. Thus, if the gage pressure is 4 oz. 
— equalling 25 lbs. — and the atmospheric pressure 
14.4 lbs. per square inch, the absolute pressure will 
be 14.65 lbs. per square inch, as shown in Fig. 
10. This must be used in all gas calculations dealing 
with change of volume due to effect of pressure. 

Failure to appreciate that the absolute pressure, 
rather than merely the gage pressure, must be used 
when computing the effect of pressure on gas vol- 
ume, or heating value content, has been responsible 
for most of the misunderstanding regarding the ef- 
fect of variation in gage pressure on gas quality and 
gas service. 



14- 



/3- 



12- 



//• 



6- 



6- 



/- 



•Lt—O- 




22 



FIGURE 11 

CURVE SHOWING EFFECT OF PRESSURE ON GAS VOLUME 
AND GAS HEATING VALUE 

§16. Differential Pressure. 

This is the difference between the pressure at the inlet and out- 
let point of a gas line. Thus, if the inlet pressure is 6 oz. and the 

//oo 




^ 



r 



I 2 3 -^ - 

&/75 P/?£5Siy/^£ //^ OZ. P£ff 5(?. /M 



23 

outlet pressure is 4 oz., the differential head, or pressure, is 2 oz. 
In gas transmission it is the differential pressure that constitutes 
the effective force for pushing the gas through the line. 



§17. What Makes Gas Flow? 

The inherent tendency of gas to expand is the basic cause of 
gas flow. Gas flow in pipes cannot take place except t)etween open- 
ings of higher to openings of lower pressure. That is, flow can be 



FIGURE 12 

CURVE SHOWING MEAN MONTHLY TEMPERATURES OF 
NATURAL GAS IN GAS MAINS AT COLUMBUS, OHIO 



60 
56 
52 
4S 
44 














y 


s. 


















/ 


/ 


s 


\ 
















/ 






> 


s, 












/ 










\ 










> 


/ 










\ 


V 


Sfc^ 






/ 














N 


4cP 
36 
52 
28 
24 
20 
/S 
/2 


^V 


\ 


/ 


f 


















X 





































































































































































































< ^ "^ ^ 



/9/7 



obtained only by sacrificing pressure. For this reason, it is a physi- 
cal impossibility to maintain uniform pressure conditions and at 
the same time have gas flow through the lines. 



24 

§18. El£Fect of Pressure on Gas Volume. 

For practical purposes, at a given constant temperature the 
volume of natural gas is inversely proportional to the absolute 
pressure — see Sec. 15 — to which the gas is subjected. That is, 
with a given mass of gas, if you double the absolute pressure you 
reduce the volume one-half, or if you double the space in which a 
given mass can expand you reduce the absolute pressure one-half. 
This is known as Boyle's Law. The small change in volume due to 
variation in gage pressure is shown in Fig. 11, and the table in 
Sec. 23. 

§19. EfiFect of Temperature on Gas Volume. 

Natural gas expands approximately 1 per cent in volume for 
each 5 degrees Fahrenheit increase in temperature, and contracts 
1 per cent in volume for each 5 degrees Fahrenheit decrease in 
temperature. The variation in mean monthly temperature of nat- 
ural gas at Columbus, Ohio, is shown in Fig. 12. 

The variation in temperature of natural gas in the underground 
mains makes more difference in the heating value than the varia- 
tion in gage pressure. The maximum fluctuation in temperature 
producing a difference in heating value of about 5 per cent, while 
the maximum fluctuation in pressure produces a difference in heat- 
ing value of less than 4 per cent. Furthermore, these variations 
work in opposite directions. That is, in winter time when the pres- 
sure is low, therefore tending to decrease the heating value, the 
temperature is low, tending to increase the heating value. This 
increase due to low temperature will always be more than the de- 
crease due to low pressure. 

§20. Standard Conditions. 

Since the volume of a gas varies with the temperature and 
pressure, in order to secure comparable results in gas calculations, 
and the establishment of standards, a standard condition is neces- 
sary. This is usually taken at 32 degrees Fahrenheit and a pres- 
sure of 29.90 inches of mercury. 

§21. Heat Unit. 

The unit quantity of heat, or the heat unit, is the quantity 
of heat required to raise the temperature of a unit weight of water 
one degree. Different kinds of units in use are as follows: The 
British Thermal Unit — B.t.u. — is universally used in America in 
engineering work. The calorie is universally used in food problems ; 
where used elsewhere it has been customary to use the expression 
"large calorie" to distinguish it from the small calorie. The 
gramme calorie, or small calorie, is universally used in scientific 
work. 

British Thermal Unit 

Abbreviated B.t.u., is the heat required to raise one pound 
of water one degree Fahrenheit. 



25 

Calorie 

This is the amount of heat required to raise one kilogram of 
water one degree Centigrade. 



Gramme Calorie 

This is the amount of heat required to raise one gramme of 
water from zero Centigrade to 1 degree Centigi'ade. 

The arithmetical relation of these three units is as follows : 



B. t. u. 
1. 

3.9682 
0.003968 



Large 
Calorie 

0.252 

1 

0.001 



Gramme 

Calorie 

252 

1 000 
1 



§22. Heating Value. 

This is the number of heat units that are evolved by the com- 
bustion of a unit weight or volume of fuel. The tei*ms "calorific 
value," "calorific power," "heating power," "thermal value," and 
"heat of combustion" are frequently applied to the same 
phenomenon. 



§23. Effect of Pressure or Temperature Changes on Heating Value 
of Gas. 

These will produce changes in volume, but will neither destroy 
nor create any heat units, and hence will neither increase nor de- 
crease the total number of heat units contained in the gas. How- 
ever, the volumetric changes will always alter the distribution of the 
total number of heat units, as follows: 



Gage 
Pressure 

Above 
Atmosphere 

8 oz. 

7 

6 

5 

4 

3 

2 

1 



Gas 
Temperature 
Fahrenheit 

65 
60 
55 
50 
45 
40 
35 



Relative 
B. t. u. 

1034 
1030 
1026 
1022 
1017 
1013 
1009 
1005 
1000 



Relative 
B. t.u. 

970 

980 

990 
1000 
1010 
1020 
1030 



Relative 
Per cent. 

103.4% 

103. 

102.6 

102.2 

101.7 

101.3 

100.9 

100.5 

100. 



Relative 
Per cent. 

97 % 

98 

99 
100 
101 
102 
103 



26 

§24. Combustion of NatursJ Gas. 

The combustible constituents of natural gas are made up of 
combinations of the elements carbon and hydrogen. When natural 
gas is burned so as to secure perfect combustion only carbon dioxide 
and water vapor are formed. That is, the carbon of the gas unites 
with the oxygen of the air forming carbon dioxide and the hydro- 
gen of the gas unites with the oxygen of the air forming water 
vapor. The water vapor, of course, will condense when cooled. 
This water vapor does not come from the gas, but is created and 
formed by the chemical action of the hydrogen in the gas and the 
oxygen in the air. 

Each cubic foot of natural gas burned requires approximately 
91/2 cu. ft. of air, forming 10 V2 cu. ft. of combustion products, 
which are made up of 2 cu. ft. of steam, 1 cu. ft. of carbon dioxide, 
and 71/2 cu. ft. of nitrogen, all thoroughly diffused through each 
other. 

FIGURE 13 

DIAGRAM SHOWING CONSTRUCTION OF 
ORDINARY GAS MIXER 




^ - • -\ (345 



The combustion of 1,000 cu. ft. of natural gas will form 2,000 
cu. ft. of water vapor or steam, and this when condensed will make 
approximately 10 1/2 gallons of water. This is not peculiar to 
natural gas, but is true of all gases containing hydrocarbon com- 
pounds. 1,000 cu. ft. of manufactured gas will form about one- 
half the water vapor produced by the combustion of 1,000 cu. ft. 
of natural gas. It is this water vapor that causes the bakers and 
broilers of stoves to rust, and where gas is used in open fires with- 
out flues, or for lighting, makes the walls and windows sweat and 
glued furniture open up. 

If the combustion is not perfect, then carbon monoxide, which 
is a deadly poison, may be formed. The toxic action of this is 
so marked that 1/10 of one per cent, is enough to produce fatal 
results. This is especially likely to be formed when a flame is 
suddenly impinged on a cold surface, as for instance the first few 
seconds operation of an instantaneous hot water heater. 

§25. Action of Gas Mixer. 

As stated in the preceding section, about 9I/2 cu. ft. of air 
must be mixed with each cu. ft. of natural gas in order to secure 
perfect combustion. In order to accomplish this the gas at a 



27 

FIGURE 14 

DIAGRAM SHOWING CONSTRUCTION OF GAS MIXER 

WITH ADJUSTABLE SPUD 



•VM-'/////M 








pressure above atmospheric air is forced through a small orifice 
by the gage pressure in the gas pipe, and thus acquires a relatively 
high velocity in passing through the small opening, as shown in 
Figures 13 and 14. In this way an aspirating action is produced 
around the orifice and this draws atmospheric air from the room 
in so that it will mingle with the gas. A gas mixer is therefore 
in effect merely a small air injector. The mixer shown in Fig. 13 
is the one most generally used, and has no adjustment for the gas. 
The mixer shown in Fig. 14 has a stationary cone and by turning 
the spud, with a wrench on the hexagonal head of the spud, the 
effective area of the orifice may be made larger or smaller, thus 
changing the velocity of the gas, and, therefore, its aspirating 
action. We did not run any tests to determine the relative merits 
of the two types of mixers. 

§26. Efficiency. 

The term "efficiency" which has become a hackneyed one on 
accounl; of its misuse, means the ratio between input and output. 
In other words, the percentage of input energy that can be ac- 
counted for on the output side of the device. 

§27. Efficacy. 

This is the power to produce an intended effect, and is en- 
tirely separate and distinct from the efficiency of the process. For 
instance, a gas burner may be efficient and yet not be effective. 
On the other hand it may be able to produce results, that is secure 
efficacy, with very low efficiency. 

§28. Cooking emd Heating Distinguished. 

In a heating operation it is merely necessary to secure perfect 
combustion in the heating device, because in so doing all of the 
available heat in the gas can be utilized. In cooking it is not only 
desirable to secure perfect combustion, but absolutely necessary to 
direct the heat to a particular place and sometimes at a particular 
time. It is for this reason that gas cooking operations are more 
susceptible to changed pressure conditions than heating operations. 

It may not be amiss to emphasize that the time element in 
many cooking operations is of much more importance than in- 
tensity. 



\ 



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